The decision by M&S to make these accommodations for Muslim workers is the latest case of freedom of religion in the workplace(Reuters)

Retail giant Marks & Spencer has faced public fury when it was revealed the company allows shop assistants the right to refuse to sell alcohol and pork products.

The news emerged after a number of customers reported that they tried to buy pork or alcohol from a Muslim shop assistant in central London, only to be told that they would have to use another till because of the cashier's religion.

Angry shoppers vented their frustration at M&S's policy on Twitter and a Facebook campaign has called for the boycott of the British brand while the official M&S Facebook page was hit by vitriolic messages from previously loyal customers.

The decision by M&S to make these accommodations for Muslim workers is the latest case of freedom of religion in the workplace and follows in a long line of discrimination law. IBTimes UK takes a look at what modern day religious discrimination in the workplace looks like and the legal implications for employers and employees.

Nadia Eweida, a Christian worker at airline giant British Airways, was asked to cover up a necklace which depicted a cross. But after Eweida refused her employer's demands, she was placed on unpaid leave. According to BA, Eweida had contravened the company's uniform policy.

After unsuccessfully taking BA on in an employment tribunal, an Employment Appeal Tribunal and the Court of Appeal. Eweida took religious discrimination case to the European Court of Human Rights. In January 2013, the court found the airline had violated Ewedia's rights by contravening Article Nine (freedom of thought, conscience and religion) of the European Convention on Human Rights.

The case highlighted some issues around the inadequacy of UK employment law concerning freedom of religion in the workplace. James Davies, who is head of the employment division at Lewis Silkin, even suggests the ruling highlights flaws in the definition of indirect discrimination.

"The exercise of trying to find a disadvantaged 'group' should be unnecessary if what law is really seeking to do is fulfil a basic principle that those with religious beliefs should be able to manifest them reasonably in the workplace," Davies argued.

The question of "reasonability" came up earlier this month in Mba V London Borough of Merton. Having initially accommodated Celestina Mba, a practising Christian care worker who adhered to the Fourth Commandment of not working on the Sabbath day (Sundays), understaffing at the Brightwell Children's Home meant that the council began to rota Mba for Sunday shifts, which Mba refused.

Mba resigned and brought a tribunal claim, claiming that the requirement to work on Sundays was discriminatory against Christians generally, and her individually, on grounds of religion or belief.

After the Employment Tribunal and Employment Appeal Tribunal dismissed Mba's appeals, she took it to the Court of Appeal. Again, the court ruled in favour of the employer but interestingly concluded that the ET's and EAT's reasoning was faulty.

However, the Lord Justices argued the conclusion the ET and EAT came to was sound and there was no other way for Brightwell Children's Home, which was open 24 hours a day seven days a week, to be run.

The case highlights that an employer does need to do everything possible to accommodate the workers' wishes and that the company's reasonable needs also need to be taken into account.

If the "reasonable test" is applied to the M&S case, it means the retailer does not have to go as far as it has in enabling workers to refuse to scan through certain goods. This is because it can reasonably accommodate staff by other means – by giving the employees work in another sector of the store, for example.

Serving customers is an integral part of a retailer's business, and it seems it would be hard for workers at similar companies to M&S to bring indirect discrimination cases against their employers for not adopting the same extensive measures as M&S (so long as that employer adopts reasonable accommodations).